Airports set minimum connecting times, which travel agents call a "legal connection," and that can be as little as 45 minutes between arrival and the departure of your connecting flight.

Normal confidence fades into an icy tingle and a clutch in my stomach. Is it time to panic?

While changing planes at London's Heathrow airport, I have more than two hours between flights, which in the past would have been enough time to leisurely find a paperback, grab a snack and use the facilities before heading to the gate for the flight home to Toronto.

But not any more.

Even though we are already in a security area, all passengers changing terminals have to go through another security screening. The queue stretches seemingly to infinity.

I watch the minutes race by, while the line barely moves. With less than an hour to go, the front of the line is still out of sight. Yes, it's panic time.

I have to persuade a surly attendant and the hundreds of furious passengers ahead of me to let me jump the queue. Even then, I almost missed the flight. From the shuttle at Terminal 4 it required an all-out sprint for 20 minutes to reach the gate. Arriving there breathless, I'm chided for arriving so close to departure time by an agent who notes that I could have been denied boarding.

And this is just one of several close calls (and missed bathroom breaks) I've encountered in recent months changing planes in North America, Europe and Asia. It's due to new delays in air travel that are not being reflected in the tickets being issued. The factors not being taken into account when connections are booked include:

• Security screening: The new world order at many airports requires even passengers who are already in a security area to queue up in snail-paced lines to be re-scanned and patted down while their shoes and laptops are X-rayed.
• Early gate closing: Airlines are strictly enforcing deadlines for passengers to be at the boarding gate. Air Canada wants passengers at the gate 25 minutes before departure; Sunwing Airline's requirement is 30 minutes. Cut it too close and your seat could be given to someone on stand-by. And some U.S. airlines are using early deadlines as a way to improve on-time performance, so the plane may push back from the gate long before the scheduled departure time.
• Baggage offloading: Tighter security in the face of fears of terrorism has led to routine X-raying and examining of checked bags — and offloading the bags of passengers who do not show. On a recent flight out of Barcelona, two passengers had checked in their bags, but could not be found after being paged in the airport. That meant their bags had to be located and unloaded from the cargo hold. The total delay was 70 minutes, ensuring that my fellow passengers and I were likely to miss our connecting flights.

The message? Build in as much cushion between flights as you can.

Whether you are flying non-stop or a connecting flight, delays are inevitable. If you must be at a destination for an important event, consider arriving a day ahead.

Airports set minimum connecting times, which travel agents call a "legal connection," and that can be as little as 45 minutes between arrival and the departure of your connecting flight. But if you accept the minimum, any delay for any reason can mean you'll miss your flight.

Travel agents are aware of the dilemma and may steer customers away from short connections that may be dicey. But increasingly customers book on-line and accept the assumptions built into the reservations computer — assumptions that haven't changed with the security-conscious times.

A good rule of thumb is add about 50 per cent more time than the recommended minimum connection time. For instance, at Toronto's Lester B. Pearson airport, the suggested minimum to switch from an international flight to a domestic one is two hours and 15 minutes, because you have to pick up your bags and go through customs and often change terminals. You're better off planning at least a three-hour layover. And that's on a normal day. Any delays due to weather or security alerts, peak traffic times or holidays might make you want to factor in more connection time.

You can get an idea of the variation in passengers waiting for connections at different times of the day and seasons of the year by looking at the website Flightstats. The site doesn't compile Canadian wait times, but will give an indication of crunch times and what's in store in an airport where you will be changing planes.

And when you fly, have your airline's 800 number handy. If you miss a connection because of delays, you're not likely to be the only one queuing up at the service desk for rebooking. Calling may let you avoid the wait in line or nab an available seat that might be given away by the time you get to the service desk to pick up the actual boarding pass.

And, of course, you can get around the connection problem by booking a non-stop flight.

It's important to know that when you look at an airline website the company's own flights are recommended first along with other partner airlines with which they have marketing alliances. So check more than one website to see if there are options that may offer a non-stop flight.

And a tip: Whether you are flying non-stop or a connecting flight, delays are inevitable. If you must be at a destination for an important event, consider arriving a day ahead. That's the advice of Mary Jean Tully, founder of The Cruise Professionals in Mississauga, Ont. She says she is amazed at how many people risk ruining their vacations by cutting it too tight on their flights. They often end up not being able to attend a big event, or in the case of embarking on a cruise, missing the boat, which could mean an end to the vacation before it starts.

Wallace Immen is a travel columnist who has been a frequent flyer for 25 years.